User Guide

AB-Access Config & User Guide 5.5 Axxcelera Broadband Wireless
July 27, 2004 Company Confidential Page 21 of 129
When performed on an AP the sector itself is quiet, so any RF energy detected must be
coming from other sources. However, when a scan is done on an SU the AP and other SUs may still
be transmitting. This may confuse the results. The RF energy from other units in the SU's sector
will be detected on-channel, but will also appear to a lesser extent in adjacent channels (e.g. 23dBm
lower than in the main channel). This should be borne in mind, and if necessary the scan should be
performed with the AP transmitter disabled, which will silence that sector (e.g. using "hmm modem
rf disable/enable").
4.10 Static Channel Scanning
This is a static-mode feature to simplify channel-changing. The feature is implemented on
SUs, and all SUs must be running 5.3.x software before this new method of channel-changing is
used, otherwise SUs will be lost when the AP is manually forced to change channel. Note that the
AP must also be running 5.3.x, so that the BID can be set to a non-zero value.
This feature is controlled by the BID and channel mask parameters. If the BID is set to zero
then the static-mode channel-scanning function is disabled. If the BID is set to non-zero then the
channel-scanning function is enabled on the SU. On booting up the SU channel and antenna are
determined by the system.conf file. A scan is initiated if the received Frame Descriptor Header
(FDHDR) error rate is greater than 90% for a rolling 3 minute period. Therefore the SU will not scan
until at least 3 minutes after booting-up, nor for 3 minutes after losing its AP. This delay allows a
reboot of the AP (even an FPGA AP with the old v2.7 Boot ROM) without causing the associated
SUs to scan.
The SU will only scan the channels defined by the channel mask, and will only detect APs
with the same BID. When the scan is complete the SU will lock to the channel/antenna that gave the
best AP signal (same BID). The SU will choose error-free channels in preference to errored ones,
and will then select the best signal level. The new channel and antenna are then automatically saved
to the system.conf file, so on rebooting the SU will start-up with the new channel and antenna
settings. Note that the current values of all parameters are saved to the system.conf file, not just the
channel/antenna parameters. If the SU does not detect any suitable signal it will revert to the
channel/antenna it was on before the scan. A further scan will occur after 3 minutes if an AP is not
detected.
The channel mask can be changed with the "hmm system mask" command, and the "hmm
radio channels" command can be used to confirm which channels will be scanned.
Until now the BID parameter in the system.conf file has been ignored by the software and a
value of zero has been used. The 5.3.x software uses the BID value defined in the system.conf file.
The BID can also now be viewed and changed with the new "hmm system bid" command. SUs can
only see APs with the same BID, so all units in a sector must have the same BID. If a unit receives a
signal from another unit which has a different BID value then only the errors from that signal appear
in the MAC stats. Valid data with the wrong BID is discarded by the receiving MAC, and does not
appear in the MAC stats.
To change the channel of a static sector using this new feature, all units must be running 5.3.x
software, must have the same non-zero BID, and each SU must only be able to see one AP with that
BID (on all channels defined by their channel mask). The channel mask on each SU should be set
appropriately, e.g. scanning all channels that are likely to be used. To change the channel of the